The present invention relates to a resettable drive mechanism for a drug delivery device and a drug delivery device comprising such a drive mechanism.
In a drug delivery device, a piston within a cartridge that contains drug may be displaced with respect to the cartridge in the distal direction by a piston rod which moves in the distal direction with respect to the cartridge. In order to provide for a reusable device, after the cartridge containing the drug has been emptied, the piston rod often has to be moved back from a distal end position to a proximal starting position. Thereby, a dose of drug can be expelled from the cartridge. U.S. Pat. No. 5,308,340 A and WO 02/053214 A1 describe injection pens, which allow to decrease a selected dose by reversing the set operation.